This invention relates to a semiconductor device containing a dielectric capacitor and a method of manufacture thereof; and, more particularly, the invention relates to a semiconductor device in which an electrode comprising Ru, RuO2 or a mixed material of Ru and RuO2 is deposited homogeneously on a substrate with a three-dimensional structure, and a method of manufacture thereof.
Semiconductor memories include a DRAM (Dynamic Random Access Memory) which is capable of high speed data rewriting. Along with progress in ultra large scale integration technology, the DRAM has entered a large capacity range of 256 M to 1 G bit. Therefore, there has been a demand for integration of circuits; and, more particularly, the size of capacitors for storing information has been made finer. Means for effecting the integration of capacitors can include reduction in the film thickness of dielectrics, selection of materials of high dielectric constant and a three-dimensional structure comprising top and bottom electrodes and a dielectric.
Among these choices, for the dielectric material, it has been known that BST having a single unit cell of perovskite structure ((Ba/Sr)TiO3) as the crystal structure has higher dielectric constant (∈) compared with SiO2/Si3N4. An example of using high dielectric materials has been reported in Japan Journal of Applied Physics, 1995, 5077p (Jpn. J. Appl. Phys., 34, 5077, 1995). According to this report, since the condition for the aspect ratio (contact hole patterns of 800 nm depth/240 nm diameter) of a three-dimensional structure using BST is about 0.65, top and bottom electrodes and a dielectric are prepared by a sputtering method.
In the prior art described above, since Pt or Ru of the bottom electrode is prepared by the sputtering method, there is a problem in that the three-dimensional structure shows poor step coverage, and adhesion to the inside wall is small compared with that to the surface and the bottom, so that a highly three-dimensional device structure with an aspect ratio of one or more can not be attained.
This invention has been accomplished to overcome the foregoing problems and has the object of providing a semiconductor device, including a dielectric capacitor having excellent step coverage in a device structure at a high aspect ratio, along with a high integration, as well as a manufacturing method of manufacture thereof.
Heretofore, although there has been a report of preparing an electrode comprising Ru, RuO2 or a mixture of Ru and RuO2 thin films by a sputtering method on a three-dimensional structure with a small aspect ratio, a film forming technique using a metalorganic chemical vapor deposition process (MOCVD) has not been taken into consideration.
The present inventors have found that a homogeneous electrode comprising Ru, RuO2 or a mixture of Ru and RuO2 thin films can be prepared on a substrate having a three-dimensional structure within a temperature range from 180xc2x0 C. or higher to 250xc2x0 C. or lower by an MOCVD process using a cyclopentadienyl complex. The principle which makes it possible to prepare a homogeneous film in the temperature range described above will be explained with reference to FIG. 5.
FIG. 5 shows a crystal structure of a ruthenium cyclopentadienyl complex used in accordance with this invention. "sgr" or xcfx80 bonds are present between a 5 membered ring and ruthenium metal, and a temperature at 180xc2x0 C. or higher is necessary as the energy of dissociation in view of the bonding energy. Further, the adhesion rate of the complex is constant on a Si substrate within a temperature range from 180xc2x0 C. or higher and 250xc2x0 C. or lower, and decompositionxe2x80x94adhesion on the surface proceeds preferentially at a higher temperature.
Accordingly, a film is formed only on the surface (top plane of protruded portions) in a substrate having a three-dimensional structure to form inhomogeneous films with the film thickness reduced on the inside wall and the bottom (top plane of convex portions). Particularly at a temperature higher than 300xc2x0 C., island crystals are formed due to a rapid decomposing reaction to form a rough film quality for which contact can not be attained. Accordingly, a homogeneous electrode comprising Ru, RuO2 or a mixture of Ru and RuO2 thin films can be formed on the surface, the bottom and the inside wall on a substrate having a three-dimensional structure by the MOCVD process using a ruthenium cyclopentadienyl complex within a temperature range from 180xc2x0 C. or higher to 250xc2x0 C. or lower.
Further, the present inventors have found that an electrode comprising Ru, RuO2 or a mixture of Ru and RuO2 thin films can be formed homogeneously by the MOCVD process using a xcex2-dietone complex within a temperature range from 300xc2x0 C. or higher to 500xc2x0 C. or lower when a structure having a three-dimensional configuration is constituted of two insulation layers, namely, a surface layer with a small adhesion rate and a inside wall layer with a large adhesion rate. The principle will be explained with reference to FIG. 2.
FIG. 2 shows a crystal structure of a ruthenium xcex2-diketone complex used in accordance with this invention. xcfx80 bonds are present between oxygen in a 6 membered ring and ruthenium metal and can dissociate at a temperature of 300xc2x0 C. or higher in view of the bond energy. However, since dissociation of an oxygenxe2x80x94carbon bond or dissociation of an oxygenxe2x80x94ruthenium bond proceeds simultaneously. the adhesion rate is small and decomposition deposition near the surface proceeds preferentially. Further, at a temperature higher than 500xc2x0 C., island crystals are formed due to violent decomposing reaction to result in a film quality that is not capable of attaining contact. Then, as shown in FIG. 3, a homogeneous electrode thin film comprising Ru, RuO2 or a mixture of Ru and RuO2 can be prepared on the surface, the bottom and the inside wall within a temperature range from 300xc2x0 C. or higher to 500xc2x0 C. or lower by an MOCVD process using a ruthenium xcex2-diketone complex on a structure having a three-dimensional configuration by constituting the structure having a three-dimensional configuration with an insulation layer consisting of a dual layered structure comprising a surface layer 31 having a small adhesion rate and a side wall layer 32 having a large adhesion rate, for example, MgO/SiO2 or Al203/SiO2 for the electrode material.
This invention has been accomplished based on the studies as described above, and it features a method of manufacturing a semiconductor device by laminating to form a bottom electrode, a dielectric and a top electrode on a substrate having a three-dimensional structure, wherein a bottom electrode and a top electrode are formed by a metalorganic chemical vapor deposition method at a temperature of 180xc2x0 C. or higher and 250xc2x0 C. or lower using a cyclopentadienyl complex as a precursor.
The cyclopentadienyl complex is used as an Ru precursor and, more particularly, dicyclopentadienyl ruthenium is preferred. The bottom electrode and the top electrode are formed each as a thin film comprising Ru, RuO2 or mixture of Ru and RuO2.
By using one Of 02, H2, N20, 03, CO and CO2 as a reaction gas, a decomposing reaction from the precursor can be promoted to form a film at a low temperature of 180xc2x0 C. or higher to 250xc2x0 C. or lower. Particularly, in a gas mixture of a reaction gas and a carrier gas (Ar, He or N2 gas), the ratio of the reaction gas to the carrier gas is preferably 1% or more.
According to this feature, an electrode thin film can be prepared homogeneously on the surface, the bottom and the side wall on the substrate having a three-dimensional structure. Accordingly, it is possible to obtain a dielectric capacitor of high integration degree comprising a top electrode/a dielectric/a bottom electrode having a three-dimensional structure of high aspect ratio of 3 or more (contact hole depth/diameter).
Further, this invention has a feature in a method of manufacturing a semiconductor device of laminating to form a bottom electrode, a dielectric and a top electrode on a substrate having a three-dimensional structure, wherein the structure having a three-dimensional constituted of an insulation film of a two-layered structure comprising a surface layer with a small adhesion rate and a side wall layer with a large adhesion rate for the starting electrode material and the bottom electrode and the top electrode are formed by metalorganic chemical vapor deposition process using a xcex2-diketone complex as the precursor at a temperature of 300xc2x0 C. or higher and 500xc2x0 C. or lower.
The xcex2-diketone complex is used as the precursor for Ru and dibivaloylmethanate ruthenium is particularly preferred. The bottom electrode and the top electrode are formed each as a thin film comprising Ru, RuO2, or a mixture of Ru and RuO2. A decomposing reaction is promoted at a temperature of 300xc2x0 C. or higher to 500xc2x0 C. or less to prepare a homogeneous electrode thin film by using one of O2, H2, N2O, O3, CO and CO2 as the reaction gas while using one of Ar, He and N2 as the carrier gas. In the gas mixture of the reaction gas to the carrier gas, the ratio of the reaction gas and the carrier gas may be 0% or more. That is, the reaction gas may or may not be used.
According to this feature, since the three-dimensional structure is constituted of two insulation layers comprising a surface layer of small adhesion rate and a side wall layer of large adhesion rate, and the electrode thin film can also be formed on the side wall to which it is less vapor deposited, an electrode thin film of uniform film thickness comprising Ru, RuO2 or a mixture of Ru and RuO2 can be prepared. Accordingly, a semiconductor device can be provided which includes a dielectric capacitor with a device structure having a high aspect ratio of 3 or more, corresponding to a high integration degree and having a step coverage performance. Particularly, when the structure comprising two insulation layers is MgO/SiO2 or Al203/SiO2, a uniform electrode thin film can be prepared depending on the different adhesion rate of the precursor.
Further, this invention features a semiconductor device having a dielectric and electrodes for applying a voltage to the dielectric in which the electrode is a thin film electrode comprising Ru, RuO2 or a mixture of Ru and RuO2 formed on a structure with an aspect ratio of the three-dimensional structure (contact hole depth/diameter) of 3 or more.
The semiconductor device can contain an electrode thin film of a uniform thickness comprising a Ru, RuO2 or a mixture of Ru and RuO2 manufactured by an MOCVD process from a cyclopentadienyl complex, or an electrode thin film of a uniform thickness comprising Ru, RuO2 or a mixture of Ru and RuO2 manufactured by an MOCVD process from the xcex2-diketone complex of high integration degree having a top electrode/dielectric/bottom electrode. Since the electrode thin film is formed homogeneously on the surface, the bottom and the side wall on the substrate having a three-dimensional structure, it is possible to obtain a dielectric capacitor of high integration degree, which is capable of functioning intactly having a three-dimensional structure of high aspect ratio. When such a dielectric capacitor is used for semiconductor devices, such as a DRAM, the capacity can be increased.
Further, this invention has a feature of forming the bottom electrode and the top electrode by a metalorganic chemical vapor deposition process of liquid carrying and evaporation using a starting solution in which a precursor containing a cyclopentadienyl complex is dissolved in tetrahydrofurane, toluene, hexane or octane. According to this feature, since the precursor can be supplied stably for a long period of time, a bottom electrode and a top electrode with good film quality can be formed and a semiconductor device with high performance can be manufactured. The method of manufacture of for the semiconductor device according to this invention is excellent for use in mass production of semiconductor devices. In the manufacturing method according to this invention, a bottom electrode, and a top electrode, which are homogeneous and of high quality, can be formed at a temperature of 180xc2x0 C. or higher and 250xc2x0 C. or lower.
Further, this invention has a feature of forming the bottom electrode and the top electrode by a metalorganic chemical vapor deposition process of liquid carrying and evaporation using a starting solution in which a precursor containing a xcex2-diketone complex is dissolved in tetrahydrofurane, toluene, hexane or octane. According to this feature, since the precursor can be supplied stably for a long period of time, a bottom electrode and a top electrode with good film quality can be formed and a semiconductor device with high performance can be manufactured. The manufacturing method for producing the semiconductor device according to this invention is excellent for use in mass production of semiconductor devices. In the manufacturing method according to this invention, a bottom electrode and a top electrode which are homogeneous and of high quality can be formed at a temperature of 300xc2x0 C. or higher and 500xc2x0 C. or lower.
When the liquid carrying and evaporation metalorganic chemical vapor deposition process using a starting solution in which a precursor containing the cyclopentadienyl complex or the xcex2-diketone complex is dissolved in a tetrahydrofuran solvent is used, since the starting solution can be stored at room temperature, thermal denaturation of the precursor as typically caused when using the sublimation method can be suppressed, and, as a result, the precursor can be supplied stably for a long period of time. The liquid carrying and evaporation metalorganic chemical vapor deposition process is a method consisting of dissolving a precursor into a solvent to prepare a starting solution, heating the starting solution in an evaporator to obtain an evaporated precursor and conducting the chemical vapor deposition process.
Further, this invention has a feature of using a solvent having a solubility of 0.05 mol/l or more for the precursor, such as tetrahydrofuran, toluene, hexane or octane. According to this feature, since evaporation of the precursor and the solvent takes place simultaneously in the evaporation step of the liquid carrying and evaporation metalorganic chemical vapor deposition process, the precursor can be supplied stably for a long period of time, which makes it possible to manufacture a semiconductor device with a higher performance.
In a case of a solvent with a solubility of 0.05 mol/l or lower, only the solvent of lower boiling point is evaporated selectively in an evaporator and, as a result, the precursor of high boiling point is deposited in the inside of the evaporator to cause clogging, making it difficult to stably supply. The solubility of the diethylcyclopentadienyl ruthenium (Ru(EtCp)2) complex as the cyclopentadienyl complex to each kind of solvent is 1.74 mol/l for tetrahydrofuran, 1.4 mol/l for toluene, 1.4 mol/l for hexane and 1.4 mol/l for octane, and the precursor can be supplied stably in the liquid carrying and evaporation metalorganic chemical vapor deposition process. Further, the solubility of the dibivaloylmethanate ruthenium (Ru(dpm)3) complex as the xcex2-diketone complex to each kind of the solvent is 0.52 mol/l for tetrahydrofuran, 0.45 mol/l for toluene, 0.27 mol/l for hexane and 0.25 mol/l for octane, and the starting material can be supplied stably in the liquid carrying and evaporation metalorganic chemical vapor deposition process.
Further, in accordance with this invention, since the organic ingredient of the precursor and the reaction gas are subjected to combustion or reductive reaction in the course of forming the film when O2, H2, CO or CO2 is used as the reaction gas, the residual carbon content in the electrode film for the bottom electrode and the top electrode can be defined as 10xe2x88x922 at % or more and 1 at % of less, by which a high quality bottom electrode and top electrode not causing contact failure can be formed, and a semiconductor device with high performance can be manufactured.
Further, this invention features a method of forming a thin film on the surface and the lateral side of a structure having a three-dimensional shape in which the structure comprises the lamination of a two layered structure consisting of a surface layer with a small adhesion rate and a side wall layer with a large adhesion rate for the starting thin film material. Use of the 2-layered structure described with reference to FIG. 3 is not restricted only to the case of forming the Ru thin film as the electrode by the MOCVD process and is generally applicable also in a film forming method, such as a sputtering method, a vacuum vapor deposition method or an MBE method as a method for forming a homogeneous film on the surface, the side wall and the bottom in a case where the film tends to be deposited preferentially only on the surface.